The invention relates to connection devices in general. More particularly, the invention relates to an interchangeable bond wire interconnect operating at radio frequencies (RF) or above that is capable of being utilized with a plurality of substrates.
Typical wireless communication devices utilize semiconductors operating at radio frequencies (RF) or above. Recently, there has been increasing demand for the use of semiconductors operating at millimeter wave frequencies. Semiconductor devices using the millimeter wave spectrum, however, are more sensitive to device parasitics than the same semiconductor devices using RF. Accordingly, the typical parasitics tolerated at lower frequencies will preclude adequate performance of devices operating at the higher millimeter wave frequencies.
One such device parasitic is the complex impedance, primarily inductance, of the bond wire interconnect used to pass electrical signals between a pair of semiconductor devices, a semiconductor device and a earner board or between two carrier boards. The bond wire is typically a gold wire or ribbon that is connected using thermal and ultrasonic energy to a first bonding or contact pad for a first semiconductor device or carrier board at the other end. Examples of the first and second semiconductor devices include different millimeter-wave Monolithic Microwave Integrated Circuits (MNIC), or a MMIC and a carrier board onto which the MMIC is directly attached, or two carrier boards. An example of a carrier board would be a microwave circuit board. Examples of a microwave circuit board include glass, alumina, duroid, quartz, FR-4, and so forth.
The significant inductive component of the bond wire operates to attenuate high frequency signals passing between the interconnected semiconductor devices unless their values are extremely low (2pif L less than  less than 1), where f is the frequency in Hertz (Hz) and L is the inductance of the bond wire in Henrys. Previous techniques have focused on reducing the length of the bond wire and chip-to-chip spacing to improve the high frequency performance of the bond wire. Manufacturing limitations, however, typically demand longer bond wire lengths and wider chip-to-chip spacing to improve the manufacturability of a specific module or multi-chip assembly (MCA).
One technique for increasing the length of the bond wire utilizes a filter theory approach to interconnect design. According to basic filter theory the bandwidth of a filter can be increased by adding more stages to the filter. This continues until adding additional stages becomes inappropriate due to unacceptable filter losses. Typically, low-pass filters are between three and seven stages. It has been previously recognized that the bond wire could be treated as a single stage low-pass filter with a fixed cutoff frequency. Consequently, the bandwidth and/or length of the bond wire could be increased by adding additional filter stages to the interconnect. Accordingly, filter-like compensation structures were added to the bonding pads to improve the high frequency response capability of the longer bond wires.
A problem occurs, however, when designing a bondwire interconnect having specific compensation structures for use in connecting two different semiconductor or microwave substrates. Specifically, the compensation structures for each millimeter-wave bondwire interconnect changes as the type of semiconductor or microwave substrate changes. For example, to interconnect a gallium arsenide (GaAs) MMIC to a glass substrate requires a specific bond wire interconnect design incorporating such factors as the type of substrate, the compensation structure, the length of the bond wire, the desired operating frequency and so forth. Each interconnect design, however, is the result of a complex and time-consuming design process. Thus, as the type of substrate changes this tedious design process must be repeated, which in turn may require modifications to the equipment used to manufacture each interconnect.
In view of the foregoing, it can be appreciated that a substantial need exists for a bond-wire interconnect to pass higher frequencies such as millimeter-wave frequencies that solves the aforementioned problems.
One embodiment of the invention comprises a method for making a bond-wire interconnect to transfer signals between different substrates. According to this process, a first compensated bond wire interconnect is made to connect two substrates of a first type at an operating frequency, the first interconnect comprising a bond-wire of a fixed length and a first pair of compensation structures formed from a low-pass filter prototype. A second compensated bond wire interconnect is made to connect two substrates of a second type at the operating frequency, the second interconnect having a bond-wire of the fixed length and a second pair of compensation structures formed from the low-pass filter prototype. A bond-wire of the fixed length, one compensation structure from the first pair, and one compensation structure from the second pair, are combined to make a third compensated bond wire interconnect to connect a substrate of the first type with a substrate of the second type at the operating frequency.
With these and other advantages and features of the invention that will become hereinafter apparent, the nature of the invention may be more clearly understood by reference to the following detailed description of the invention, the appended claims and to the several drawings attached herein.